I'm also 19! And I also forgot to mention, I believe the minimum hours you need are 1250 to get maternity leave. If you don't qualify, you can still arrange something with your boss, you could temporarily switch to prn and work one shift a month until you're ready to return in order to keep your job.
It depends on how many hours you have there. I was told I barely qualified for fmla and I have over 1400 hours at my work, which is also in elderly care! I didn't tell my boss until I was around 25 weeks, and everything was fine! I'm also part time so I only qualified for 6 weeks of leave, but it's better than nothing! Good luck!